This invention relates to a system for denitrating nitric acid solution of plutonium nitrate, uranyl nitrate, or mixture thereof and continuously calcinating the denitrated material by irradiating the same with microwaves to produce plutonium oxide, uranium oxide, or mixture thereof to be used as a nuclear fuel.
One typical example of a conventional denitration device is described hereunder in conjunction with FIG. 1. The denitration device of a batch furnace type shown in FIG. 1 generally comprises a heating vessel 1 and a turn table 3 which forms a bottom plate of the vessel 1 and is moved vertically and rotated by rotating means, not shown, through a shaft 2 connected to the turn table 3. On the turn table 3 is disposed a dish-shaped boat 5 which contains a solution 4 to be irradiated and heated by microwaves generated by a microwave generator, not shown, through a wave guide 6 connected to the upper wall of the vessel 1. Vapor and gases generated in the vessel 1 in the heating process are exhausted through a duct 7 to an external exhaust gas treating system. The denitrated product obtained in the boat 5 after the heating process is scratched off and fed into a calcinating vessel, not shown, in which the scratched denitrated product is calcinated at a constant temperature.
Usually, in the denitration process carried out by using a device of the type described above, a temperature of a material to be treated varies with heating time and is represented by FIG. 2.
Referring now to FIG. 2, the temperature of the nitrate solution gradually rises by the continuous irradiation of the microwaves to a time when it reaches about 100.degree.-120.degree. C. which is represented by a point A in FIG. 2. In this time, the concentration is caused by the vaporization of water and nitric acid at 100.degree.-120.degree. C. After the solution has been concentrated to some extent (point B in FIG. 2), the temperature increases and, at 350.degree.-400.degree. C., the denitration reaction proceeds and a denitrated product is finally produced. The denitrated oxide is then calcinated in a calcinating furnace.
However, since the denitration device described hereinbefore is of a batch type, it is difficult to treat a large amount of the solution so that it takes much time to raise or lower the temperature of the calcinating furnace. Moreover, it is troublesome to scratch off and take out the denitrated product and to transfer it into a calcinating furnace located at a different position.